Specialization, tolerance, memory, competition, latency, and strife among T cells

Mixed lymphocyte reaction induced by multiple alloantigens and the role for IL-10 in proliferation inhibition

The frequency of T cells that can respond to alloantigens is unusually high. It remains unclear how T cells would respond when stimulated by multiple major histocompatibility complex (MHC) disparate alloantigens in the same cultures. In this report, we examined potential interactions of T cell clones that were stimulated simultaneously by two sets of complete MHC disparate alloantigens using mixed lymphocyte reaction (MLR). In this assay, we observed that proliferation of B6 lymphocytes (H-2b) stimulated by both BALB/c (H-2d) and C3H (H-2k) allogeneic cells was not increased but rather reduced as compared to B6 cells stimulated with either BALB/c or C3H allogeneic cells. Interestingly, interleukin (IL)-10 expressions at both protein level and mRNA level was significantly increased in cultures stimulated with the two MHC alloantigens, while IL-2, tumor necrosis factor (TNF)-α, transforming growth factor (TGF)-β1 production did not show any differences. In addition, Foxp3 mRNA expression was comparable amongst all groups. In conclusion, we observed an inhibitory effect in T cell proliferation in response to multiple MHC mismatched alloantigens in MLR, and this effect might be associated with the upregulation of IL-10 expression.

Serotonin transporter in lymphocytes of rats exposed to physical restraint stress

OBJECTIVES

Glucocorticoids and stress cause transcriptional and functional changes on the serotonin transporter (SERT) in the central nervous system. Stress can produce specific modifications of SERT in lymphocytes, which could be associated with alterations in immune response. The aim of this study was to evaluate the effect of a physical restraint stress protocol on (1) rat lymphocyte proliferation in the presence of the selective serotonin reuptake inhibitor fluoxetine and (2) SERT kinetic parameters, i.e. binding capacity (Bmax), affinity (Kd) and Hill coefficient (nH).

METHODS

Male adult Sprague-Dawley rats were placed in Plexiglass boxes (5 h daily for 5 days), and blood was obtained by cardiac puncture on day 6. Serum corticosterone was quantitated by an immunoenzymatic assay. Lymphocytes were isolated by density gradients and adhesion to plastic, of which there was sufficient material for further experiments, then cultured with or without the mitogen concanavalin A (Con A, 2 μg/ml) and fluoxetine (1-50 μM). Cell proliferation was measured with tetrazolium salts, and [(3)H]paroxetine was used as a SERT-specific ligand for binding assays.

RESULTS

Restraint produced a significant increase in serum corticosterone of stressed rats. The proliferative response to Con A was similar in the controls and stressed animals. Fluoxetine reduced cell proliferation with and without Con A. Restraint diminished the inhibitory effect of fluoxetine on proliferation. Restraint also increased Bmax and Kd, but decreased nH. Treatment of rats with actinomycin D, a transcription inhibitor, reduced Bmax in stressed animals.

CONCLUSIONS

Restraint stress modulated the effect of fluoxetine on cell proliferation, probably through the modification of the presence and the function of SERT.

To B or not to B: role of B cells in pathogenesis of arthritis in HLA transgenic mice

Population studies have shown that amongst all the genetic factors linked with autoimmune disease development, MHC class II genes are the most significant. Experimental autoimmune arthritis resembling human rheumatoid arthritis (RA) can be induced in susceptible strains of mice following immunization with type II collagen (CIA). We generated transgenic mice lacking endogenous class II molecules and expressing various HLA genes including RA-associated, HLA-DRB1*0401 and HLA-DQ8, and RA-resistant, DRB1*0402, genes. The HLA molecules in these mice are expressed on the cell surface and can positively select CD4+ T cells expressing various Vβ T cell receptors. Endogenous class II invariant chain is required for proper functioning of the class II transgene. Arthritis development in transgenic mice is CD4+ and B cells dependent. Studies in humanized mice showed that B cells are required as antigen presenting cells in addition to antibody producing cells for the development of CIA. The transgenic mice expressing *0401 and *0401/DQ8 genes developed sex-biased arthritis with predominantly females being affected, similar to that of human RA. Further, the transgenic mice produced autoantibodies like rheumatoid factor and anti-cyclic antibodies. Antigen presentation by B cells leads to a sex-specific immune response in DRB1*0401 mice suggesting a role of B cells and HLA-DR in rendering susceptibility to develop arthritis in females.

Delineating the role of the HLA-DR4 "shared epitope" in susceptibility versus resistance to develop arthritis

In humans, HLA-DR alleles sharing amino acids at the third hypervariable region with DRB1*0401(shared epitope) are associated with a predisposition to rheumatoid arthritis, whereas DRB1*0402 is not associated with such a predisposition. Both DRB1*0402 and DRB1*0401 occur in linkage with DQ8 (DQB1*0302). We have previously shown that transgenic (Tg) mice expressing HLA-DRB1*0401 develop collagen-induced arthritis. To delineate the role of "shared epitope" and gene complementation between DR and DQ in arthritis, we generated DRB1*0402, DRB1*0401.DQ8, and DRB1*0402.DQ8 Tg mice lacking endogenous class II molecules, AE(o). DRB1*0402 mice are resistant to develop arthritis. In double-Tg mice, the DRB1*0401 gene contributes to the development of collagen-induced arthritis, whereas DRB1*0402 prevents the disease. Humoral response to type II collagen is not defective in resistant mice, although cellular response to type II collagen is lower in *0402 mice compared with *0401 mice. *0402 mice have lower numbers of T cells in thymus compared with *0401 mice, suggesting that the protective effect could be due to deletion of autoreactive T cells. Additionally, DRB1*0402 mice have a higher number of regulatory T cells and show increased activation-induced cell death, which might contribute toward protection. In DRB1*0401.DQ8 mice, activated CD4(+) T cells express class II genes and can present DR4- and DQ8-restricted peptides in vitro, suggesting a role of class II(+) CD4 T cells locally in the joints. The data suggest that polymorphism in DRB1 genes determines predisposition to develop arthritis by shaping the T cell repertoire in thymus and activating autoreactive or regulatory T cells.

Serum analysis after transplant nephrectomy reveals restricted antibody specificity patterns against structurally defined HLA class I mismatches

This study deals with HLA-mismatched kidney transplants that have been removed following rejection. Sera from 27 patients were screened for HLA-specific antibodies by direct complement-dependent lymphocytotoxicity with HLA-typed cell panels. Circulating donor-specific antibodies were detected in 3 cases (11%) before and in 26 cases (97%) after allograft nephrectomy. These findings demonstrate the production of donor-specific antibodies in patients with rejected transplants, but in most cases, they were undetectable before nephrectomy, because the graft had adsorbed them. With an HLAMatchmaker-based serum analysis program, we observed restricted antibody specificity patterns against amino acid triplet-defined epitopes on donor HLA-A,B antigens. Many donor triplets were non-reactive while others were apparently recognized by antibodies. In some patients, the donor triplet specific antibodies persisted for a long time whereas in many other patients, they became undetectable after a few months. The characterization of the antibody specificity profiles of post-allograft nephrectomy sera is clinically useful in defining criteria of HLA mismatch acceptability for sensitized patients awaiting another transplant. It provides also opportunities for determining the relative immunogenicity of mismatched triplets.

Human dendritic cells genetically engineered to express cytosolically retained fragment of prostate-specific membrane antigen prime cytotoxic T-cell responses to multiple epitopes

The ability of two plasmid DNA vaccines to stimulate lymphocytes from normal human donors and to generate antigen-specific responses is demonstrated. The first vaccine (truncated; tPSMA) encodes for only the extracellular domain of prostate-specific membrane antigen (PSMA). The product, expressed following transfection with this vector, is retained in the cytosol and degraded by the proteasomes. For the "secreted" (sPMSA) vaccine, a signal peptide sequence is added to the expression cassette and the expressed protein is glycosylated and directed to the secretory pathway. Monocyte-derived dendritic cells (DCs) are transiently transfected with either sPSMA or tPSMA plasmids. The DCs are then used to activate autologous lymphocytes in an in vitro model of DNA vaccination. Lymphocytes are boosted following priming with transfected DCs or with peptide-pulsed monocytes. Their reactivity is tested against tumor cells or peptide-pulsed T2 target cells. Both tPSMA DCs and sPSMA DCs generate antigen-specific cytotoxic T-cell responses. The immune response is restricted toward one of the four PSMA-derived epitopes when priming and boosting is performed with sPSMA. In contrast, tPSMA-transfected DCs prime T cells toward several PSMA-derived epitopes. Subsequent repeated boosting with transfected DCs, however, restricts the immune response to a single epitope due to immunodominance.

HLA-DRB1*0402 (DW10) transgene protects collagen-induced arthritis-susceptible H2Aq and DRB1*0401 (DW4) transgenic mice from arthritis

To investigate the role of HLA-DR4 in predisposition to arthritis, we generated transgenic mice carrying DRB1*0401 and DRB1*0402 genes. We have previously shown that DRB1*0401 molecule renders B10.RQB3 (H2A(q)) mice susceptible to porcine and human type II collagen-induced arthritis. We report that the introduction of DRB1*0402 transgene does not lead to development of arthritis in mice when they are immunized with porcine and human type II collagen. In addition, DRB1*0402 protects B10.RQB3 mice against developing arthritis with bovine type II collagen. These data show that DRB1 can modulate the disease mediated by A(q). In vivo depletion of DRB1*0402 did not lead to induction of collagen-induced arthritis in transgenic mice. In vitro cytokine analysis shows that mice protected from collagen-induced arthritis produce lower amounts of Th1 and higher levels of Th2 type cytokines upon immunization with type II collagen. Protection of mice was also related to higher apoptosis in DW10 mice as indicated by higher amounts of BclII in response to type II collagen. On the basis of our observations in HLA transgenic mice, we hypothesize that DRB1 polymorphism can modulate disease by shaping the T cell repertoire in thymus and select autoreactive T cells.

123I-Interleukin-2: biochemical characterization and in vivo use for imaging autoimmune diseases

We describe in detail the labelling of interleukin-2 with I ( I-IL2), its biochemical characterization, the binding assay and its use for the detection of tissues infiltrated with mononuclear cells. Human recombinant IL2 was labelled using an enzymatic method and its biochemical characterization was performed using high performance liquid chromatography (HPLC) analysis of cyanogen bromide-cleaved protein. biological and binding assays were performed on CTLL-2 cell line and on activated peripheral blood lymphocytes. studies were performed 1 h after administration of 2-3 mCi of I-IL2 in 10 newly diagnosed type 1 diabetes patients, five pre-diabetic patients, 10 Hashimoto's thyroiditis patients, 10 coeliac disease patients and 10 normal volunteers. I-IL2 scintigraphy allowed the detection and quantification of activated mononuclear cells in several affected tissues. In detail, I-IL2 accumulation was detected in the thyroid of all patients affected by Hashimoto's thyroiditis, in the bowel of all coeliac disease patients and in the pancreas of all pre-type 1 diabetic patients. By contrast, in newly diagnosed type 1 diabetics, I-IL2 scan was positive in five of the 10 studied patients. I-IL2 scintigraphy may be useful for studying autoimmune phenomena and in diagnostic protocols to evaluate the presence of other tissue involvement in patients with an organ-specific autoimmune disease.

The immunological synapse

The immunological synapse plays a central role in organising the immune system. Through their synaptic activity both T and B cells usually, but not always, acquire the information that critically determines the level and nature of the responses that they make. For T cells much of that information comes from epicrine and paracrine cell-cell interactions in the cluster that forms around a dendritic cell. These interactions are being dissected by experiments in which two populations of TCR-transgenic T cells are combined in vivo. Another important aspect of synaptic activity is the way in which different levels of expression of MHC class II molecules influence Th1/Th2 balance. In exploring this form of control we are learning something of general importance about cis-regulation.

Roles of cytotoxic T-lymphocyte-associated antigen-4 in the inductive phase of oral tolerance

To elucidate the roles of cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) in oral tolerance, we studied the consequences of CTLA-4 blockade during the inductive phase of oral tolerance using a transgenic T-cell transfer model. We found that CTLA-4 blockade significantly accelerated cell cycle progression of antigen-specific T cells and dramatically increased their numbers in lymphoid organs following oral administration of ovalbumin (OVA). In mice fed with OVA, only approximately 35% of specific T cells underwent more than four cycles of cell division. This was increased to 65% in mice fed with OVA and treated with a blocking anti-CTLA-4 monoclonal antibody (mAb). The OVA-specific T cells in the latter group were localized primarily in the T-cell zones of the mesenteric lymph nodes and Peyer's patches with a few penetrated into B-cell follicles. Nevertheless, both faecal anti-OVA immunoglobulin A (IgA) and seral anti-OVA immunoglobulin G (IgG) were produced in anti-CTLA-4 mAb-treated mice. These results suggest that CTLA-4 limits the degree of T-cell activation by blocking cell cycle progression during the inductive phase of oral tolerance. In the absence of the CTLA-4 signal, mucosal exposure of antigen induces heightened T-cell activation and expansion, which in turn promotes the production of antigen-specific antibodies.

The stress protein BiP is overexpressed and is a major B and T cell target in rheumatoid arthritis

OBJECTIVE

The ubiquitously expressed intracellular protein formerly designated p68 has been identified as autoantigen at both the antibody and the T cell level in rheumatoid arthritis (RA).

METHODS

We used 2 independent approaches, Edman degradation and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry, to characterize p68, and we compared its features with those of the endoplasmic reticulum stress protein BiP.

RESULTS

In synovial sections from RA patients, BiP was highly overexpressed as compared with control sections. Under in vitro stress conditions, BiP was found to translocate to the nucleus and the cell surface. BiP-specific autoantibodies were present in 63% of 400 RA patients, in 7% of 200 patients with other rheumatic diseases, and in none of the healthy subjects. Thus, BiP-specific autoantibodies represent a new diagnostic marker in RA. Furthermore, we found that BiP-specific T cell reactivity was altered in RA. In healthy individuals and patients with other rheumatic diseases, BiP-reactive T cells were undetectable. In RA, overt T cell reactivity to BiP was observed or could be induced by specifically blocking antigen presentation to potentially regulatory T cells.

CONCLUSION

Since overexpression of BiP has been shown to decrease the sensitivity of cells to killing by cytotoxic T cells, BiP overexpression and BiP-specific autoimmunity may be involved in the pathogenesis of RA.

T cells compete for access to antigen-bearing antigen-presenting cells

These studies tested whether antigenic competition between T cells occurs. We generated CD8(+) T cell responses in H-2(b) mice against the dominant ovalbumin epitope SIINFEKL (ova8) and subdominant epitope KRVVFDKL, using either vaccinia virus expressing ovalbumin (VV-ova) or peptide-pulsed dendritic cells. CD8(+) T cell responses were visualized by major histocompatibility complex class I-peptide tetrameric molecules. Transfer of transgenic T cells with high affinity for ova8 (OT1 T cells) completely inhibited the response of host antigen-specific T cells to either antigen, demonstrating that T cells can directly compete with each other for response to antigen. OT1 cells also inhibited CD8(+) T cell responses to an unrelated peptide, SIYRYGGL, providing it was presented on the same dendritic cells as ova8. These inhibitions were not due to a more rapid clearance of virus or antigen-presenting cells (APCs) by the OT1 cells. Rather, the inhibition was caused by competition for antigen and antigen-bearing cells, since it could be overcome by the injection of large numbers of antigen-pulsed dendritic cells. These results imply that common properties of T cell responses, such as epitope dominance and secondary response affinity maturation, are the result of competitive interactions between antigen-bearing APC and T cell subsets.

An intra-Peyer's patch gene transfer model for studying mucosal tolerance: distinct roles of B7 and IL-12 in mucosal T cell tolerance

Development of mucosal immunity and tolerance requires coordinated expression of a number of genes within the mucosa-associated lymphoid tissue (MALT). To study the roles of these genes in the MALT, we have established a MALT-specific gene transfer model using replication-defective adenovirus as vector. In this model, the target gene of interest is directly delivered into the Peyer's patch by intra-Peyer's patch injection of the recombinant virus. Using this gene transfer model, we investigated the roles of B7-1 and IL-12 in the development of mucosal tolerance. We found that intra-Peyer's patch injection of OVA induced Ag-specific T cell hyporesponsiveness, as manifested by decreased T cell proliferation and IL-2/IFN-gamma production upon subsequent immune challenge. Intra-Peyer's patch B7-1 gene transfer at the time of OVA administration partially reversed the inhibition of T cell proliferation and IL-2 secretion, but had no effect on IFN-gamma production. By contrast, intra-Peyer's patch IL-12 gene transfer completely restored T cell proliferation and IFN-gamma secretion and partially reversed IL-2 inhibition. Using an adoptive TCR transgenic model, we further demonstrated that B7 and IL-12 played distinct roles during the inductive phase of mucosal tolerance. B7 selectively increased T cell proliferation and IL-2 secretion without affecting IFN-gamma production, whereas IL-12 increased both IL-2 and IFN-gamma production. These results indicate that B7 alone may not be sufficient to abrogate mucosal tolerance, and that cytokines such as IL-12 may also be required. Based on these findings, we propose a new model to explain the paradoxical roles of B7 in mucosal immunity and tolerance.

HLA class II transgenic mice as models of human diseases

Predisposition to develop various autoimmune disorders has been associated with certain HLA class II molecules but there is a lack of information on the pathophysiological role of HLA genes in conferring susceptibility. Various experimental animal models of autoimmune disease have been studied to address the role of immune response genes. To study the interactions involved between class II molecules (DQ and DR) and define the immunologic mechanisms in various diseases, we generated HLA-DR and DQ transgenic mice that lacked endogenous class II molecules. The HLA molecules in these mice are expressed on the cell surface and can positively select CD4+ T cells expressing various V beta T-cell receptors (TCR). A peripheral tolerance is maintained to transgenic HLA molecules thus indicating that these molecules act as self. Mouse co-stimulatory and accessory molecules can interact with the HLA-peptide-TCR complex leading to efficient T-cell activation. In this review, we describe immunogenetic models for human diseases using these transgenic mice. Our studies show that HLA class II transgene-restricted T cells recognize the immunodominant antigens and peptide epitopes, similar to HLA class II-restricted human T cells. Thus these mice provide powerful tools to understand the role of HLA class II molecules in predisposition and onset of human diseases and to develop immunotherapy and vaccines.

Autoimmunity, immunologic tolerance, and gene therapy

Research in our laboratory focuses on three major themes: 1. Costimulation and cell death in autoimmunity. 2. Molecular mechanisms of immunologic tolerance. 3. Gene therapy of autoimmune diseases. We have performed a large series of experiments using T cell receptor (TCR) transgenic mice examining mechanisms of autoimmunity and peripheral T cell tolerance. A major focus of our current research is to understand the roles of costimulation and cell death in T cell tolerance and T cell-mediated autoimmune diseases. This involves studies of the TCR, the costimulatory molecules, and the cytokines. We are also exploring novel strategies for the treatment of autoimmune diseases by gene transfer.

VLA-4 expression on peripheral blood lymphocytes is downregulated after treatment of multiple sclerosis with interferon beta

Adhesion molecules are likely to play a critical role in the immunopathogenesis of multiple sclerosis (MS). The interaction of vascular cell adhesion molecule-1 (VCAM-1) with its lymphocyte ligand very late antigen-4 (VLA-4) may mediate migration of lymphocytes into the CNS. We have previously demonstrated that MS patients treated with interferon beta (IFN-beta) have a significant increase in soluble VCAM-1 (sVCAM-1) soon after the initiation of treatment, and this effect correlated with the resolution of contrast-enhancing MRI lesions. We studied the cell surface expression of VLA-4 by flow cytometry in 10 MS patients before and during IFN-beta treatment. We found a significant decrease in mean VLA-4 fluorescence of MS patients' lymphocytes on treatment and no change in untreated controls. In vitro treatment of lymphocytes with IFN-beta did not reproduce this effect, but the addition of sVCAM-1 did result in a decrease in VLA-4 expression. These data indicate that the previously identified increase in sVCAM-1 may lead to a decrease in VLA-4 expression and that this effect may partially explain the mechanism of action of IFN-beta.

Human T-cell response to myelin basic protein peptide (83-99): extensive heterogeneity in antigen recognition, function, and phenotype

Multiple sclerosis (MS) is considered a T cell-mediated autoimmune disease, and myelin proteins are the most likely candidate autoantigens. Based on experiments performed in experimental allergic encephalomyelitis (EAE), innovative immunotherapies have been developed that target either the specific trimolecular complex of encephalitogenic T cells, consisting of T-cell receptor (TCR), major histocompatibility complex (MHC; HLA in humans) class II molecule, and autoantigenic peptide, or the effector functions of these cells. To provide the basis for the transfer of these specific immunotherapies to MS, we extensively characterized the human T-cell response to one major myelin epitope, the myelin basic protein peptide (83-99). We analyzed restriction element, TCR usage and affinity, fine specificity, cytokine production, cytolytic activity, and expression of surface molecules on 41 T-cell clones (TCCs) derived from MS patients and normal controls. We demonstrate a high degree of complexity of recognition patterns as well as of functional phenotypes among T cells responding to the same epitope. In contrast to results from animal models, these findings indicate that the design of epitope-based specific immunotherapies for MS is more difficult than previously thought.

The importance of the back-signal from T cells into antigen-presenting cells in determining susceptibility to parasites

It has long been known that certain MHC class II genes can dominantly suppress immune responses and so increase susceptibility to parasite infections, but the mechanism has been unclear. Recent work has revealed one way in which this form of suppression may operate, through gating by MHC class II molecules of the back-signal from activated T cells into macrophages. The two known suppressive genes of the mouse are expressed in macrophages more extensively than are other class II genes. This is associated with suppression of IL-4 production resulting, we infer, from overproduction in the macrophages of IL-12, the counter-cytokine to IL-4. The lack of IL-4 may itself be immunosuppressive, even for Th2 responses, and excess IL-12 can overinduce the antiproliferative cytokine IFN-gamma. Although this mechanism requires further substantiation, we believe that it offers a reasonable answer to an old conundrum.

The development of technetium-99m-labelled interleukin-2: a new radiopharmaceutical for the in vivo detection of mononuclear cell infiltrates in immune-mediated diseases

We describe here a new method for labelling interleukin-2 (IL-2) in high specific activity with 99mTc for in vivo studies in man. Labelling was performed via a two-step reaction using an N3S bifunctional chelating agent. To optimise the reaction, factors affecting the incorporation of 99mTc into the N3S ligand were studied. The conjugation of the preformed N3S chelate ligand to IL-2 was then similarly optimised. Various strategies for purifying the 99mTc-IL-2 were explored including size-exclusion, ion-exchange, and several modes of reversed-phase chromatography. The radiochemical purity of the purified protein was determined by HPLC, ITLC, TCA precipitation, and SDS-PAGE. The receptor binding capacity of 99mTc-IL-2 was studied. Biodistribution studies in normal mice were performed with 99mTc-IL-2 purified using different techniques or labelled after prolonged storage and compared to 125I-IL-2.

Rheumatoid arthritis: autoreactive T cells recognising a novel 68k autoantigen

OBJECTIVE

A 68k autoantigen has been identified by specific antibodies from patients with rheumatoid arthritis (RA). This study considered whether or not this antigen is a target for T cells and thus may play a part in T cell mediated immunopathology of active RA.

METHODS

The 68k antigen was isolated and used in a nitrocellulose bound form to stimulate T cells. Proliferation of T lymphocytes of peripheral blood as well as synovial fluid was measured.

RESULTS

Peripheral blood T cells specifically proliferating against the 68k antigen were detected in 19 of 27 patients with RA (70%). For T cells isolated from peripheral blood, proliferation peaked on day 10. When T cells were isolated from actively inflamed synovial fluid, the proliferation kinetics shifted to a peak on day 3. Blockade of HLA class II antigens resulted in an increase of proliferation in the case of HLA-DP. Applying HLA-DP specific antibodies capable of inhibiting antigen presentation mediated by this molecule, T cells of 17 of 27 RA patients (63%) proliferated to a higher extent than with the 68k antigen alone. The phenomenon that an increased proliferation occurred upon blockade of a particular HLA class II family member was also demonstrated for DQ and DR: the 68k antigen likewise stimulated T cells restricted for DP or DQ, respectively.

CONCLUSIONS

The novel 68k antigen is a target of both T and B cellular immune responses and as such could play a part in the immune dysfunction of RA. The finding that blocking of certain HLA class II molecules functioning in antigen presentation (for example, via HLA-DQ) results in a higher instead of lower proliferation in vitro, may argue for the presence of antigen specific suppressive T cells.

CD45RC isoforms define two types of CD4 memory T cells, one of which depends on persisting antigen

The cellular basis of immunological memory remains a controversial area with respect to the identity of memory T cells and the role of persisting antigen. CD4 T cells are phenotypically divided by the expression of high and low molecular weight isoforms of CD45, surface markers that are frequently used to identify "naive" (CD45Rhigh) and "memory" (CD45Rlow) subsets. The latter subset responds rapidly in antigen recall assays but paradoxically has a short life span, a property that is difficult to reconcile with long-term memory. The present study examines these issues using a DTH (delayed-type hypersensitivity) model in which contact sensitivity to dinitrochlorobenzene (DNCB) was transferred to athymic nude rats by recirculating CD4 T cell subsets defined in the rat by the anti-CD45RC mAb OX22. As expected, CD45RC+ (but not RC-) CD4 T cells from normal unprimed rats transferred a DNCB-specific DTH response, whereas, 4 d after sensitization the CD45RC- (memory) subset alone contained the DNCB reactivity. However, when donor cells were collected from thymectomized rats sensitized two mo earlier, DNCB-specific responses were transferred by both CD45RC- and RC+ subsets suggesting that many of the latter had developed from cells with a memory phenotype. This was confirmed when CD45RC CD4 T cells from 4-d primed rats were parked in intermediate nude recipients and recovered 2 mo later. DNCB-specific activity was now found wholly within the CD45RC+ "revertant" subset; the CD45RC-CD4 T cell population was devoid of activity. Importantly, we found that the total switch-back from CD45RC- to RC+ could be prevented, apparently by persisting antigen. The results indicate that there are two functionally distinct categories of memory T cells: one, a short-lived CD45Rlow type which orchestrates the rapid kinetics, the other, a longer-lived CD45Rhigh revertant which ensures that immunological memory endures.

Alteration of a model antigen by Au(III) leads to T cell sensitization to cryptic peptides

Certain metal ions are known to be potent sensitizers, but the self proteins modified by metal ions and the self peptides recognized by 'metal-specific' T cells are unknown. In humans and mice treatment with gold anti-rheumatic drugs, containing Au(I), may lead to allergic and autoimmune side effects. Human and murine T cells do not react to Au(I), however, but to the reactive metabolite Au(III). Here we show that alteration by Au(III) of a model antigen, bovine ribonuclease (RNase)A, results in T cell sensitization to cryptic peptides of this protein. Upon immunization of mice with Au(III)-pretreated RNase [RNase/Au(III)], CD4+ T cell hybridomas specific for RNase/Au(III) were obtained in addition to those recognizing the immunodominant peptide RNase 74-88; the latter also were obtained after immunization with native RNase. RNase/Au(III)-specific T cell hybridomas reacted against RNase/Au(III) and RNase denatured by S-sulfonation of cysteine residues, but not against native RNase, or RNase pretreated with Au(I), A1(III), Cu(II), Fe(II), Fe(III), Ni(II), Mn(II), or Zn(II). Using a panel of overlapping, synthetic RNase peptides which were devoid of gold or gold-induced modifications, epitope mapping revealed that RNase/Au(III)-specific T cell hybridomas recognized the cryptic peptides 7-21 and 94-108, respectively. Comparison of the proliferative response of bulk CD4+ T cells, prepared from splenocytes after immunization with either RNase/Au(III) or native RNase, revealed that Au(III) pretreatment of RNase led to a markedly enhanced response to the two cryptic peptides while it did not influence the response to the immunodominant peptide. The cryptic peptides were also presented after preincubation of bone marrow-derived macrophages with RNase and Au(I), but not with RNase alone, suggesting that oxidation of Au(I) to Au(III) and subsequent protein alteration by Au(III) can happen in mononuclear phagocytes. We conclude that Au(III) alteration of proteins alters antigen processing and, thus leads to presentation of cryptic peptides. This mechanism may shed light on the development of allergic and autoimmune side effects of Au(I) anti-rheumatic drugs. In addition, it might provide a general mechanism of how metal ions act as T cell sensitizers.

Defective expression of the apoptosis-inducing CD95 (Fas/APO-1) molecule on T and B cells in IDDM

Triggering of CD95 (Fas/APO-1) cell surface receptors regulates the elimination of autoreactive T and B lymphocytes through a mechanism of cell suicide called apoptosis. Three different mutations involving CD95 or its ligand are responsible for induction of autoimmunity in susceptible mouse strains. To determine whether a defect involving the CD95 receptor is associated with human insulin-dependent diabetes mellitus (IDDM), we have studied the expression of CD95 on peripheral blood mononuclear cells from IDDM patients at different stages of the disease. Three-colour flow cytometry and mean fluorescence analysis showed that T and B lymphocytes from newly diagnosed IDDM and patients with long-standing disease, and subjects at high risk of developing the disease were highly defective in CD95 expression (p < 0.001), whereas monocytes from all the groups studied expressed normal amounts of CD95 molecules on their cell surface. T-cell subset analysis showed that the impairment of CD95 expression in IDDM patients and high-risk subjects involved both CD3+ CD4+ (p < 0.001) and CD3+ CD8+ cells (p range: < 0.01-0.001), suggesting that this alteration concerns both helper and cytotoxic T cells. Moreover, after activation in vitro with anti-CD3 monoclonal antibody, T cells from newly diagnosed IDDM patients maintained a reduced CD95 expression during the entire cell culture period (24-72 h) in comparison to the control population (p < 0.001). In conclusion, we found a reduced expression of the apoptosis-inducing CD95 receptor on T and B lymphocytes of individuals with clinical and preclinical IDDM. We hypothesize that this defective expression may impair the capacity of autoreactive lymphocytes to undergo CD95-mediated apoptosis, contributing to the lack of control on beta-cell specific B- and T-cell clones.

Modulation of T-cell adhesion markers, and the CD45R and CD57 antigens in human alcoholics

Direct and indirect evidence indicates that T cells are altered in alcoholics. The most commonly reported changes under direct examination have been consistent with an increased level of activation as reflected by shifts in the ratio of common leukocyte antigen isoforms expressed at the cell surface, by increases in the expression of class II antigen, or by alterations in the expression of various adhesion molecules. Functional evidence for T-cell abnormality includes loss of delayed hypersensitivity and a number of findings attributed to dysregulation of B cells by alcoholic T cells; these include the widely reported distrubances of immunoglobulin production in vivo and a range of abnormal responses when T and B cells are combined in vitro. Detailed flow cytometric examination of T cells from alcoholics with or without active liver disease reveals a significant loss of L-selectin CD8+ T cells, but not usually of CD4+ T cells. There is an inverse increase in the expression of CD11b on the CD8+ cells that have decreased L-selectin+ percentages. Both CD8+ and CD4+ T cells in alcoholics display a significant loss of the CD45RA isoform and a gain of cells exhibiting the CD45RO isoform. Other surface alterations include increased expression of CD57, a marker most commonly associated on T cells with conditions of chronic increased antigenic exposure. It is argued that these and other T-cell alterations in alcoholics are cytokine-driven in part and result in T-cell differentiation states that are functionally inappropriate.(ABSTRACT TRUNCATED AT 250 WORDS)

Association of H2Ab with resistance to collagen-induced arthritis in H2-recombinant mouse strains: an allele associated with reduction of several apparently unrelated responses

HLA class II alleles can protect against immunological diseases. Seeking an animal model for a naturally occurring protective allele, we screened a panel of H2-congenic and recombinant mouse strains for ability to protect against collagen-induced arthritis. The strains were crossed with the susceptible strain DBA/1, and the F1 hybrids immunized with cattle and chicken type II collagen. Hybrids having the H2Ab allele displayed a reduced incidence and duration of the disease. They also had a reduced level of pre-disease inflammation, but not of anti-collagen antibodies. The allele is already known to be associated with reduction of other apparently unrelated immune responses, suggesting that some form of functional differentiation may operate that is not exclusively related to epitope-binding. It is suggested that this may reflect allelic variation in the class II major histocompatibility complex promoter region.

Modulation of helper T cell function by prostaglandins

OBJECTIVE

To determine the influence of prostaglandins on the production of interleukins 2, 4, and 5 (IL-2, IL-4, and IL-5), interferon-gamma (IFN gamma), granulocyte-macrophage colony-stimulating factor, and transformating growth factor beta 1 by CD4+ T cells.

METHODS

TH0, TH1, and TH2 T cell clones were stimulated in the presence and absence of the prostaglandin E1 (PGE1) analog misoprostol and PGE2. Lymphokine production was analyzed by using a semiquantitative polymerase chain reaction with lymphokine-specific primer sets and/or by determining lymphokine activity in bioassays.

RESULTS

PGE2 and misoprostol have distinct effects on different functional T helper cells. TH1 cells, which predominantly produce IL-2 and IFN gamma, are completely inhibited, while TH2 cells, which preferentially produce IL-4 and IL-5, are largely unaffected. Misoprostol and PGE2 are equivalent in their ability to modulate T cell function. In the presence of prostaglandins, TH0-like helper cells, which are characterized by the coproduction of multiple lymphokines, function as TH2 cells; however, they do not differentiate into TH2 T cells.

CONCLUSION

Prostaglandins that are produced in inflamed tissue can regulate the functional capabilities of infiltrating T cells. In the presence of PGE2, TH1-like responses are suppressed and TH0-like responses are shifted toward a TH2-like pattern dominated by the production of IL-4 and IL-5. Inhibition of prostaglandin production by antiinflammatory agents might restore TH1 responses with local production of IL-2 and IFN gamma.

The development of humoral immunological memory to a T-cell-dependent antigen requires thymic emigrant cells

Immunological memory is embodied in the rapid and enhanced immune responsiveness to previously encountered antigens. Classically, memory would depend on the presence of small resting long-lived specific lymphocytes which, through clonal expansion after priming with antigen, would be present at higher frequencies than in naive animals. Here we report that T-cell-reconstituted athymic mice, which lack recent thymic emigrants, mount a primary response to a T-cell-dependent antigen, but do not develop memory or the capacity to produce specific anti-TNP IgG1 antibodies during the secondary immune response. On the other hand, if thymocytes are continuously provided during the secondary response, a typical secondary immune response is achieved with high levels of specific IgG1. These results lead us to propose that the development of humoral immunological memory cannot be explained solely by the long life span of primed T lymphocytes, but is rather a dynamic state dependent on the continuous presence of recent thymic emigrants and qualitative functional differences in responder T cells.

T cells are responsible for the enhanced synovial cellular immune response to triggering antigen in reactive arthritis

In reactive arthritis (ReA) there is specific proliferation of synovial fluid (SF) mononuclear cells (MNC) to the triggering bacterial antigen; comparatively little or no response is seen in peripheral blood (PB). To investigate the mechanism of this elevated local immune response, we examined patients with typical ReA who showed an enhanced antigen-specific synovial immune response in bulk culture. Using separated fractions of T cells and antigen-presenting cells (APC) from PB and SF we showed that the synovial T cells rather than SF APC are responsible for the specific proliferation. By limiting dilution analysis, the frequency of T cells responding to the specific antigen was found to be significantly increased compared with the frequency of irrelevant antigen-specific T cells. Furthermore, the frequency of T cells responding to the specific antigen was higher in SF (between 1/619 and 1/4846, mean 1/2389) than in PB (between 1/1286 and 1/16,279, mean 1/7350). We conclude that the specific synovial cellular immune response in ReA is mainly due to an expansion of antigen-specific T cells within the joint. However, the non-specific hyper-reactivity of SF T cells and differences between SF and PB APC may make a more minor contribution.